The present invention relates to power saving of computer apparatuses, peripheral devices, and other electronic apparatuses, and in particular to energy saving of a disk array unit connected to a computer apparatus.
The disk array unit is a peripheral device of a computer apparatus, and is used as an external storage unit for storing data of the computer. A plurality of magnetic disk units are mounted on the disk array unit. When the disk array unit and a computer system serving as a host unit of the disk array unit are functioning, all of a plurality of magnetic disk units mounted on the disk array unit are typically operating.
In the specification of the present application, a term “operating” means that a magnetic disk unit is ready to response immediately when control information or data is inputted to the magnetic disk unit from a control unit for a host unit. It is now assumed that the magnetic disk unit is in the so-called sleep mode and a magnetic disk medium is in the still state. When a time required or the magnetic disk medium to be spun up to its ordinary number of revolutions has elapsed, the magnetic disk unit responds. This case is not included in the scope of the term “operating”. Furthermore, the term “operating” does not include the case where the magnetic disk unit is in the power saving mode and it responds after the power saving mode has been canceled.
Furthermore, when viewed from a magnetic disk unit, the term “access” means whether a command intended for itself has been issued or whether information giving and receiving intended for itself has been requested. Typically, it corresponds to that in response to an instruction of information acquisition or storage of a host unit, a signal is issued from an electronic circuit of the host unit side including a drive interface to a magnetic disk unit intended for.
When an access from a host unit has occurred, the magnetic disk unit to be accessed must be operating so as to be capable of transmitting or receiving control information, the magnetic disk unit to be accessed must be operating. On the other hand, in the case where there is no access from a host unit or a control unit, it is not necessary to keep the magnetic disk unit in the “operating” state.
For magnetic disk units, there is typically a control method including the steps of throwing the power supply upon receiving access from a host unit, rotating a magnetic recording medium, and answering to the access (transmitting or receiving information), and gradually cutting the power supply of predetermined electronic circuits and a motor for rotating the magnetic recording medium after the answering has been finished. In other words, the magnetic disk unit has various power saving modes built-in, and has a function of selecting a predetermined power saving mode according to mainly the frequency of access from a host unit or a control unit, and automatically shifting into that mode.
In a conventional disk array unit, mounted magnetic disk units or magnetic disk units so set as to be recognizable from a host unit are controlled so as to become operating in response to start of the disk array unit. After the disk array unit has been started, the above described magnetic disk units mounted thereon remain operating until the power supply of the disk array unit is cut. If such manipulation as to cut the power supply of the disk array unit is conducted, such a sequence as to shift the magnetic disk units from the “operating” state to power supply off-state functions in response to the manipulation, and thereafter the power supply of the disk array unit is cut.
As for magnetic disk units which have not been so set as to be recognizable from a host unit and magnetic disk units mounted as spares, the power supply is thrown and a magnetic disk unit is made “operating”, when a magnetic disk unit is so set as to be recognizable from a host unit or a magnetic disk unit for spare is used. Once a magnetic disk unit is made operating, the power supply is not cut individually until the power supply of the disk array unit is cut. In the case of a magnetic disk unit having an increased number of magnetic disk units, such as a disk array unit having several hundreds magnetic disk units connected, therefore, a power saving measure becomes indispensable.